Trifluoromethanesulfonate salt of 5,10,15,20-tetrakis(1-benzylpyridin-1-ium-4-yl)-21H,23H-porphyrin and its CaII complex

The synthesis and crystallization of a trifluoromethanesulfonate salt of 5,10,15,20-tetrakis(1-benzylpyridin-1-ium-4-yl)-21H,23H-porphyrin, C68H54N8 4+·4CF3O3S·4H2O, 1·OTf, are reported. The asymmetric unit contains half a porphyrin molecule, two trifluoromethanesulfonate anions and two water molecules of crystallization. The macrocycle of tetrapyrrole moieties is planar and unexpectedly it has coordinated CaII ions in occupational disorder. This CaII ion has only 10% occupancy (C72H61.80Ca0.10F12N8O16S4).

The synthesis, crystallization and characterization of a trifluoromethanesulfonate salt of 5,10,15,20-tetrakis(1-benzylpyridin-1-ium-4-yl)-21H,23H-porphyrin, C 68 H 54 N 8 4+ •4CF 3 SO 3 À •4H 2 O, 1•OTf, are reported in this work.The reaction between 5,10,15,20-tetrakis(pyridin-4-yl)-21H,23H-porphyrin and benzyl bromide in the presence of 0.1 equiv. of Ca(OH) 2 in CH 3 CN under reflux with an N 2 atmosphere and subsequent treatment with silver trifluoromethanesulfonate (AgOTf) salt produced a red-brown solution.This reaction mixture was filtered and the solvent was allowed to evaporate at room temperature for 3 d to give 1•OTf.Crystal structure determination by singlecrystal X-ray diffraction (SCXD) revealed that 1•OTf crystallizes in the space group P2 1 /c.The asymmetric unit contains half a porphyrin molecule, two trifluoromethanesulfonate anions and two water molecules of crystallization.The macrocycle of tetrapyrrole moieties is planar and unexpectedly it has coordinated Ca II ions in occupational disorder.This Ca II ion has only 10% occupancy (C 72 H 61.80 Ca 0.10 F 12 N 8 O 16 S 4 ).The pyridinium rings bonded to methylene groups from porphyrin are located in two different arrangements in almost orthogonal positions between the plane formed by the porphyrin and the pyridinium rings.The crystal structure features cation� � �� interactions between the Ca II atom and the �-system of the phenyl ring of neighboring molecules.Both trifluoromethanesulfonate anions are found at the periphery of 1, forming hydrogen bonds with water molecules.

Chemical context
Porphyrins are heterocyclic organic macrocycles; they are composed of four pyrrole subunits interconnected at their �-carbon atoms through methine bridges.(Lee et al., 2018) The structure of porphyrin can be found in nature, such as in various types of chlorophylls and hemes.Chlorophylls play a fundamental role in photosynthesis as light-gathering antennas and as charge-separation reaction systems.Hemes are one of the key components of biocatalysts and oxygen carriers in the blood.Without porphyrins, there can be no life on earth.(Hiroto et al., 2017) Porphyrin has an expanded electronic structure of 18 �-electrons; the resulting aromaticity gives rise to unique photophysical and semiconductor properties that make these compounds have a wide range of applications, which include artificial photosynthesis, catalysis, molecular electronics, sensors, non-linear optics, and solar cells (Lee et al., 2018;Cook et al., 2017).They are also useful in medicine as photosensitizers in the photodynamic therapy of cancer (PDT) and in the treatment of some bacterial infections (Uttamlal & Sheila Holmes-Smith, 2008).
For the past ten years, the motif of tetrapyridylporphyrin in its free base (TPyP) and metalated form (MTPyP) has been one of the most used basic components in building blocks in the design of structural solids based on porphyrins in materials chemistry since it has a flat and rigid structure, bearing laterally divergent pyridyl groups prone to supramolecular interaction with neighboring entities (Seidel et al., 2011;Lipstman & Goldberg, 2009a,b, 2010;Koner & Goldberg, 2009).In this work, the periphery of tetrapyridylporphyrin was modified by the benzylation of the pyridyl groups, obtaining the tetracationic salt of triflate 5,10,15,20-tetrakis(1-benzylpyridin-1ium-4-yl)-21H,23H-porphyrin, 1•OTf, which was studied as a fluorescent chemosensor for iodide in pure water in its bromide salt form (1•Br) published in a previous work (Salomo ´n-Flores et al., 2019).In this paper, we describe the most important structural characteristics of the 1•OTf crystal, which presents positional disorder, since 90% of the crystal is made up of free-base porphyrin while 10% of the crystal the tetrapyrrolic nucleus is coordinated to a Ca II ion.

Structural commentary
Compound 1•OTf crystallizes in the monoclinic system in space group P2 1 /c (Fig. 1).The asymmetric unit consists of half the 1•OTf molecule, two triflate anions to neutralize the charge, and two water molecules of crystallization.The atoms of the triflate molecules are in partially occupied sites.The degree of occupational disorder of the crystallization molecules such as water, triflate and tosylate are common in crystals of 5,10,15,20-tetrakis (1-methylpyridinium-4-yl) cationic porphyrins (Lourenc ¸o et al., 2011;Makowski et al., 2012).
The C-C(meso), C-C and C-N bond lengths and angles in the pyrrole rings are in the ranges of 1.337 (2) to 1.451 (2) A ånd 105.18 (12) to 126.89 (12) � , respectively, which are in the average ranges of bond lengths and angles reported for mesopyridyl porphyrins.These macrocycle dimensions are relatively constant for all porphyrins, including complex multiporphyrins, as well as the simpler derivatives of porphyrin (Konarev et al., 2018;Cook et al., 2017) The tetrapyrrole macrocycle is characteristically rigid and flat; the deviations of the individual atoms from the mean plane of the 24-membered porphyrin core range from 0.004 (1) (C1) to 0.060 (2) A ˚(C8), the core of 1•OTf is flatter than 1•Br, 100% free base, with values of atomic deviations from 0.012 (N1) to 0.094 A ˚(N2).The four pyridinium rings in the meso positions are in two different arrangements.The first pyridinium ring forms an almost orthogonal arrangement between the plane of the 24-membered porphyrin and the pyridinium ring N3/C11-C15 with an angle between the planes of 85.1 (3) � , while the second pyridinium ring N4/C23-C27 forms an angle between the planes of 61.54 (6) � .These angles are large due to the steric hindrance by the benzyl groups and their values are similar to those of 1•Br of 81.3 and 57.3 � .Likewise, the benzyl groups are almost perpendicular to the corresponding pyridiniums, the angles between their planes The molecular structure of 1•OTf.The atoms of the asymmetric unit are labeled.Hydrogen atoms, except for the -NH pyrroles, have been omitted for clarity.
being 77.1 (3) and 84.32 (1) � for the two benzylpyridinium fragments.The dihedral angle between the adjacent pyrrole rings N1/C1-C4 and N2/C6-C9 is 4.90 (9) � .The planes of the pyrrole rings are inclined to the N 4 plane by 3.03 (7) � (N1/C1-C4 ring) and 4.71 (7) � (N2/C6-C9 ring), therefore the overall degree of distortion of the macrocycle is moderate and there is also no significant effect of the benzyl groups on the planar geometry of the porphyrin.

Supramolecular features
The porphyrin macrocycle of 1•OTf presents �-electron deficiency as a result of the multiple positive charge of the Nbenzylpyridinium groups and is stabilized mainly by electrostatic interactions with the triflate anions; however, other supramolecular interactions also stabilize the crystal.
The N-benzylpyridinium groups in 1•OTf produce steric hindrance, which prevents the aggregation of porphyrin molecules and �-� stacking interactions between the tetrapyrrolic nuclei, which are common in free-base tetrapyridylporphyrins (Seidel et al., 2011;Lipstman & Goldberg, 2009b, 2010).Conversely, salts of tetrapyridinium porphyrins quaternized with small groups such as -CH 3 and -H generate porphyrin molecules offset-stacked; this cofacial arrangement is a wellknown feature of the supramolecular interporphyrin organization.However, bulky groups as substituents in the meso positions of the porphyrins can hinder the interactions between porphyrins (Lourenc ¸o et al., 2011;Makowski et al., 2012;Wang et al., 2013;Zhao et al., 2013), as in this case.
The crystallographic results of 1•OTf show that each porphyrin molecule binds to four neighboring porphyrin units through C-H� � �� and �-� interactions.The N3-benzylpyridinium fragments are involved in C13-H13� � �� interactions (Table 1)  The molecular structure of 1•OTf-Ca.The atoms of the asymmetric unit are labeled.Hydrogen atoms have been omitted for clarity.

Figure 3
The interaction of one porphyrin unit with four neighboring units through C-H� � �� contacts and �-� interactions.pyridinium ring N3/C11-C15 adjacent to the positive charge (N + ).According to the geometric parameters of Csp 2 -H� � ��systems, this interaction is considered strong because the C13-H13� � �� distance is 2.65 A ˚and the C-H� � �� angle is 164 � (Nishio, 2011;Nishio et al., 2014;Brandl et al., 2001).The �-� interaction is through the stacking of the benzyl group bonded to the N4/C29-C34 pyridinium ring, where the centroid-centroid distance is 4.345 (4) A ˚. Fig. 3 shows the interaction of a porphyrin unit with four neighboring units through C-H� � �� contacts and �-� interactions between the pyridinium and terminal phenyl groups.
Those interactions in 1•OTf lead to the formation of twodimensional square-grid networks in which the squares are formed by N4-benzylpyridinium groups (green), while the N3benzylpyridinium groups (blue) are placed inside each square and are separated from each other by 4.01 A ˚.This di-periodic lattice is illustrated in Fig. 4. Di-periodic square grid networks are common in free-base tetrapyridylporphyrins (Lipstman & Goldberg, 2009a, 2010).
In contrast to 1•OTf-Ca, the phenyl group (C29-C34) bonded to the N4-pyridinium ring has a cation� � �� interaction leading to di-periodic square-grid networks (Fig. 5).The Ca 2 + � � � � distance is 3.897 A ˚(distance between the cation and the centroid of the �-ring), � � 45 � (the most preferred geometry is when the cation is on the �-system where � = 0 � ) and � = 13.761� (� is the dihedral angle between the planes of the �-system and that of the cation), which are within the geometric parameters of the cation-� interaction (Yamada, 2020;Borozan et al., 2013).Fig. 4 illustrates the Ca 2+ � � �� interaction in spacefilling mode.complexes, revealed that no structures have been reported thus far (April 2024).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The hydrogen atoms of the C-H and N-H bonds were placed in idealized positions whereas the hydrogen from water molecules were localized from the difference electron density map and their position was refined with U iso tied to the parent atom with distance restraints (DFIX) U iso (H) = aU eq (parent atom) where a is 1.5 for -CH 3 and N-H moieties and 1.2 for others.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

Figure 4
Figure 4Square-grid two-dimensional lattice pattern observed in 1•OTf.The N4benzylpyridinium and N3-benzylpyridiniums groups are in green and blue, respectively.Hydrogen atoms have been omitted for clarity.

Table 2
Experimental details.